A syngas generator is a device that can convert a fuel reactant and an oxidant reactant into a gas stream containing hydrogen (H2) and carbon monoxide (CO), commonly referred to as syngas. The reactant mass flow rates are controlled to vary the composition, for example the equivalence ratio or oxygen-to-carbon (O/C) ratio, of the reactant mixture supplied to the syngas generator. The O/C ratio affects various factors during the operation of the syngas generator, for example, operating temperature, carbon (soot and coke) formation and the composition of the product syngas stream.
In some syngas generator applications, an oxidant reactant is supplied with passive flow control, while supply of a fuel reactant is actively controlled by a variable flow control device. The flow rate of the oxidant reactant that is supplied via the passive control device can vary, but the variation is essentially uncontrolled. This approach, with active control of only one reactant, offers the advantages of variable flow control, rapid response times, reduced system complexity and reduced cost. For example, an oxidant can be supplied via a fixed orifice device, while a fuel is metered by a variable speed fixed displacement pump controlled by a controller and optionally corresponding sensors. An example of a syngas generator system is described in U.S. Patent Application Publication No. 2006/0048502 A1 published Mar. 9, 2006 (Ser. No. 11/193,930 filed Jul. 29, 2005), entitled “Integrated System For Reducing Fuel Consumption And Emissions In An Internal Combustion Engine”.
In load-following or transient applications, the requirement for a product syngas stream and/or the supply of an oxidant reactant to a syngas generator can vary rapidly. For example, in an exhaust after-treatment system of a diesel powered vehicle, a syngas generator can be employed to produce a product syngas stream to regenerate components of the exhaust after-treatment system, while a portion of the exhaust stream from the diesel engine can be used as the oxidant reactant stream for the syngas generator. In this example application, the temperature, pressure and composition of the exhaust stream from the diesel engine, and the requirement for syngas to regenerate the exhaust after-treatment system, can vary rapidly. A control method capable of responding rapidly to such changes is required in order to maintain the appropriate supply of oxidant and fuel reactants to provide that parameters, such as, for example, the equivalence ratio or oxygen-to-carbon (O/C) ratio are kept within a desired range during operation of the syngas generator. This is to reduce or prevent undesirable effects such as excess carbon formation, excess fuel consumption, and excessive temperatures, during the operation of the syngas generator.
One approach to controlling the supply of a fuel reactant to a syngas generator is based on a closed-loop, or feedback only, control regime. For example, the flow rate of fuel reactant supplied to the syngas generator can be controlled and dynamically adjusted in response to signals from sensors located in the product syngas stream. A shortcoming of this approach is slow response time, for example, due to the thermal mass of the syngas generator and delays caused by the sensors. Another approach is based on an open-loop, or feed-forward only, control regime, using modeled or pre-determined information to anticipate the requirements of the syngas generator. An example of a feed-forward control regime in an exhaust after-treatment system of a diesel engine is one in which certain operating parameters of the engine are used to determine the requirement for fuel reactant supplied to the syngas generator (for example, via a look-up table). A shortcoming of this approach is that the desired accuracy may not be achieved, and the control system may not respond appropriately to an unusual operating situation.
The present control regime for controlling reactant supply to a syngas generator overcomes at least some of the shortcomings of these prior approaches and offers additional advantages. An advantage of the present approach is that the control regime is capable of responding rapidly, and with a reduced variance from the desired reactant supply value, during steady-state and transient conditions in load-following applications.